Field of the Invention
The present invention relates to a control apparatus for a vehicle including a drive system, and to a vehicle.
Description of the Background Art
Generally, when a vehicle is braked while traveling, reduction of the speed of a rotational inertia body of a drive system causes a torsional torque T to be applied to the drive system. Particularly in the case where the vehicle includes a sub transmission in addition to a main transmission such as automatic transmission and the transmission is in a low gear as well as where the vehicle has a hybrid system including, in addition to an engine, a motor generator (hereinafter referred to as MG) having a large moment of inertia, torsional torque T applied to the drive system is excessively large. Thus, in order to ensure an adequate parts strength for addressing such an excessively large torsional torque, it is necessary to increase the parts size. An example of the hybrid system is a single-MG hybrid system including only one MG (see for example Japanese Patent Laying-Open No. 2014-184923).
Torsional torque T applied to the drive system is conceptually represented by T=Ieq×(ω1−ω0/Δt (Ieq: equivalent moment of inertia, ω: angular velocity of rotational body, Δt: unit time). The equivalent moment of inertia from the engine to the transmission is represented by Ieq=Ie×λ×λ (Ie: moment of inertia from the engine to the transmission input, λ: total gear ratio of the transmission). It is seen from this equation as well that in the case of the hybrid system and in the case where the sub transmission is in the low gear for example, the equivalent moment of inertia is large and therefore torsional torque T applied to the drive system when the vehicle is braked is large.
In order to address such a problem, some conventional four-wheel drive vehicles shift the transmission to a higher gear when it is determined that drive wheels spin. In this way, the torque applied from the drive wheels to a powertrain (transmission, torque converter, and clutch for example) when the vehicle is braked suddenly can be suppressed (see for example Japanese Patent Laying-Open No. 2009-210000). Here, the powertrain is a transmission mechanism transmitting a torque between a drive source (engine, MG, and the like for example) and drive wheels. The drive system includes the drive source and the powertrain.